Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

[txbandit44]

I am looking to junk the 77 70hp johnny and move to a modern 4 stroke on my 73 starcraft Super sport. Will the mount hole match?

 

[Texasmark]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

I'm not answering your question and you gave no specifics so anyone attempting to answer has nothing to go on.

What I do have to say is that you need to think real hard about what you said in your title. I run 2 strokes. But I have picked up on here the fact that 4 strokes don't have the hole shot the the others do. Couple that with the fact that you downsized your engine by 30% which will make it worse and in addition you just lost your top end, you might ask yourself if you are doing the right thing.

I am a human (I think) and human nature is funny in that if you never had it you don't miss it, but if you have you can't help but miss it.

Think about it. The money spent will be gone forever but you'll probably have what you bought with it for many years.

Mark

 

[WIMUSKY]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

I can't answer the holes matching or not question either, but as Texasmark said, there will be a big drop in performance.

 

[txbandit44]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

Thank you both. You are correct i should have clarified that question. I would like to know if the transom mount holes on a 1977 70 hp motor match a modern merc yamaha honda or suzuk 50 hp. I have piloted a similar boat with a 50 hp 4 stroke its good enough for me. So i have addressed my performance concerns.

 

[steelespike]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

Off the top of my head I would say a 36 year old motor mount won't even be close.
Hopefully someone will have personal experience and be able to help.

 

[roscoe]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

OMC/Johnson/Evinrude used the standard bolt mounting pattern before it became the standard.
The rest of the industry adopted the BIA standard, one by one, by about 1980, Mercury by the mid 80's.

My 1973 Evinrude 65 hp uses the standard BIA holes.

I would say they will match.


Here are the measurements of the BIA standard.

Top 2 holes are 12 7/8" apart.
Bottom 2 holes are 9 7/8" apart.
Top to bottom, 8".


Click thumbnail to enlarge.

 

[Bill3434]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

OMC/Johnson/Evinrude used the standard bolt mounting pattern before it became the standard.
The rest of the industry adopted the BIA standard, one by one, by about 1980.

My 1973 Evinrude 65 hp uses the standard BIA holes.

I would say they will match.


Here are the measurements of the BIA standard.

Top 2 holes are 12 7/8" apart.
Bottom 2 holes are 9 7/8" apart.
Top to bottom, 8".


Click thumbnail to enlarge.

View attachment 187554

That's good to know.

I like my 70hp 77 Johnny, I'll give it up when it dies.

 

[Texasmark]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

That's good to know.

I like my 70hp 77 Johnny, I'll give it up when it dies.

Smart move my man!

Mark

 

[Bill3434]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

Smart move my man!

Mark

I think so too, especially when I see the price tag of a new engine. Besides I get a kick out of towing someone with a new engine onto shore. Sucks when I'm towed but I got an excuse, my engine is old.

 

[seahorse5]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

I had a '73 StarCraft SuperSport 16 for many years. You ought to consider the 75 or 90hp E-TEC on the back. Some of the older SS 16 boats were only rated for 85, but the 75 E-TEC does a good job, is super quiet, and there is no smoke at all. You may be disappointed with the anemic low end torque on the mid-size 4-strokes that are available.

The mounting hole standard used today is based on the 1960 Johnson-Evinrude 75hp bolt pattern.

 

[SigSaurP229]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

No the mount holes will not match other brands I know Merc mounts won't match at all. There is absolutely no possible way I would trade a 77 2 stroke moter for a new 4 stroke under any circumstance especially a lower hp motor.

 

[BonairII]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

I vote for NOT getting the 50hp motor. Slower and heavier than the 2-stroke 70hp.

 

[82rude]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

i went from a 90 evinrude to a 2011 60hp etec and after getting use to a little less speed im happy.actually 10 plus mph less but who,s counting.i look at it as a older 1982 motor that was still good but getting on in years vs a new motor .i travel 27miles one way up a lake/res to camp several times a month,plus fishing which comes out to 90 miles approx (low of 75)everytime.plus i looked at my age( 54)
retired also, so that 60 is most likely my last motor till dirtnap time.i dont know the weight or hp rating of your starcraft so i wont speak to that .my boat is cedarstrip and is very light and strong .it is very happy with a wide range of motors .most boats need to be within the recommended 70 percent hp range to be happy but not mine .i think its 70 per anyways.actually im within min specs but ive seen the same boat with a 30 yammy and lots in the muskokas use 40s and still move along good.your choice .go etec though, not 4 poke.editing post to add that orginal rating fore my boat was 75 hp but due to total redo from stem to stern its legally registered and rated for 90 hp as a homemade boat.

 

[roscoe]

Re: Repower from a 70 hp Johnny to a newer 50 HP 4 stroke

No the mount holes will not match other brands I know Merc mounts won't match at all. There is absolutely no possible way I would trade a 77 2 stroke moter for a new 4 stroke under any circumstance especially a lower hp motor.

Omc from way back, are a match to Yamaha, Mercury, Mariner, for 1985 and newer. They all match now.